Thursday, October 28, 2010

Ancient Timbers Reveal Secrets of Anasazi Builders

Bijal P. Trivedifor National Geographic Today

September 28, 2001

Some of America's earliest high-rise architects lived in Chaco Canyon,
New Mexico, between the tenth and twelfth centuries. Here these Anasazi
designers and engineers built 12 great houses up to five stories high
with hundreds of rooms. However, where the Chaco residents harvested the
lumber for these enormous buildings is a question that has stumped
archaeologists. Now scientists have found a way to let ancient timbers
tell their secrets.

Geochemist Nathan English, of the University
of Arizona, has developed a chemical test to determine the origin of
these trees.

"Like people, trees are what they eat," says English, who analyzed the wood from the Chaco dwellings.

In the same way that human bones absorb and store calcium from food, trees take up the element strontium. Exactly how much is absorbed depends on the quantity in the surrounding soil and rock where the tree grows.

The test is based on comparing ratios of two strontium isotopes from wooden construction beams in the Chaco houses with measurements taken from modern trees in the surrounding mountain ranges.

"It's like a modern paternity test for trees," said English.

The 12 Chaco dwellings together contain about 200,000 wooden beams that were used to construct the roofs. But the Chaco Canyon is an almost treeless landscape that was certainly never the source of the timber.

When English analyzed the strontium ratios from the timber used to construct the houses, they matched those from spruce and pine trees located on mountaintops up to 60 miles (100 kilometers) away in the Chuska and San Mateo mountain ranges.

It is amazing that the Chaco dwellers carried thousands of these enormous logsmost of which measured about 5 meters (15 feet), about 22 cm (9 inches) in diameter and weighed about 275 kilograms (600 pounds)for up to one hundred kilometers, said English.

"These findings amplify our suspicions that these people were tremendously well organized and socially powerful," says archaeologist Jeffrey Dean, also of the University of Arizona. It takes a lot of determination and coordination to harvest logs from up to 100 kilometers away and bring them back to the village, he added.

English's team also found wood within single rooms that came from both the Chuska and San Mateo mountains, and that trees from different great houses were harvested in the same year.